MATERIALS SCIENCE AND ENGINEERING SEMINAR Evaporation-Assisted Alignment of CdSe/CdS Nanorods at a Millimeter/Centimeter Scale by Ruihong Zhang Ph.D. Prelim Part I Exam Advisor: Prof. C. Handwerker ABSTRACT Cadmium selenium (CdSe) and cadmium sulfide (CdS) nanorods have been studied widely due to their unique optical properties, such as linearly polarized emission and large global Stokes shift. In order to utilize their anisotropic optical and electrical properties and increase the total emission, the alignment of nanorods needs to be achieved at millimeter/centimeter scale for device applications, such as polarized light emitting diodes. Among various assembly methods, evaporation-assisted self-assembly has demonstrated promise in organizing nanorods into highly ordered structures. Smectic liquid crystal and crystalline structure in which nanorods are aligned with orientational and positional ordering have been successfully fabricated from colloidal of nanorods. In this study, a critical analysis is conducted between these two assembly structures in terms of assembly conditions, assembly dimensions, and the degree of alignment. In contrast to the smectic liquid crystal structure, the crystalline structure is favored for device applications due to higher packing density and more controllable alignment structure. For assemblies with crystalline structures, the influence of important parameters including the substrate type and condition, the rod aspect ratio, and the rod concentration are summarized. Since current studies lack of quantitative characterization of alignment of nanorods, Fourier transform and 2D X-ray diffraction analysis are proposed for the measurement in small- and large-scale assemblies, respectively. Additionally, an in-situ observation using environmental cell transmission electron microscope (ETEM) is proposed in order to understand the influence of the evaporation rate on the dynamic local assembly and the final structure, and rationalize the possible phase transition from smectic to crystalline structures. Date: Wednesday, October 24, 2012 Time: 1:30 PM Place: ARMS 3115 PURDUE MSE [cid:image003.png@01CDAD15.1E1E67C0] Lisa Stacey Secretary/Development Assistant Purdue University School of Materials Engineering 765/494-4100
